The present application claims priority from Japanese application No. P2000-238816, filed Aug. 7, 2000, the disclosure of which is hereby incorporated by reference herein.
The present invention relates to a light scanner and a projection display device using the light scanner. More particularly, the present invention relates to a light scanner which is such as to provide a low-cost precise display of an image projected onto a large screen that realizes high definition and high color reproducibility, and a projection display device using the light scanner.
Laser beam displays provide high laser-beam monochromaticity and high laser-beam output ability. They are expected to, for example, realize a wide color reproduction range and be used as large-screen displays with higher brightness. They are also drawing attention as one possible candidate for home-theater high-definition/large displays.
Hitherto, beam scanning systems have been used in laser displays. In laser displays using beam scanning systems, a polygon mirror which rotates at a high speed so as to be in synchronization with a horizontal synchronization signal of an image signal is used to carry out horizontal scanning using a modulated laser beam. After the horizontal scanning, a galvanometer mirror is driven so as to be in synchronization with a vertical synchronization signal of an image signal through a relay lens in order to perform vertical scanning using the modulated laser beam, so that an image is projected onto a screen through a projection lens.
A beam scanning system in which a modulated laser beam is used for horizontal scanning (or line scanning) by a polygon mirror, and in which the modulated laser beam is used for vertical scanning (or frame scanning) by a galvanometer is proposed in detail in, for example, xe2x80x9c200 Inches Full Color Laser Projection Display,xe2x80x9d SPIE vol. 3296, pp. 116-25, 1998, by Y. Hwang et al. The beam scanning system provides features such as making it possible to project an image onto a surface of any shape, change the size of an image, and change a projection direction.
Increasing the definition of a display image inevitably causes an increase in the amount of information displayed. Therefore, it is desirable that a large number of pixels be provided with the capability of allowing a display of a large number of pieces of color information. For example, for beam-scanning-type high-definition display devices, it is desirable that they be capable of, for example, allowing an increase in an image signal band and an increase in a scanning frequency. However, in the case of beam scanning systems using mechanical scanning systems, it is considerably difficult to increase scanning frequency.
More specifically, according to the above-described proposal, when a polygon mirror having 24 surfaces is rotated at a speed of 39,375 rpm, a horizontal scanning frequency of 15.75 kHz is obtained when the NTSC (National Television System Committee) system is used. However, when this signal standard is applied to the HDTV (High Definition Television) system that features 1920xc3x971080 60 fr/Progressive Scan, the required number of rotations is 162,000 rpm, which is approximately 4 times that in the NTSC system.
Accordingly, the technology of high-speed rotation of a horizontal scanning system using a polygon mirror has many problems that need to be solved, so that, for example, stabilization of operation during high-speed rotation and angular precision of a reflecting surface of the polygon mirror need to be achieved.
In order to realize a higher-speed beam scanning system at a low cost, a method of using a very small optical mirror having rapid response in the scanning system is drawing attention.
A very small optical mirror can mechanically provide rapid response due to an increase in device rigidity resulting from the very small size of the device and due to a reduction in the moment of inertia. This rapid response reaches a value on the order of up to 120 MHz.
Therefore, when a very small optical mirror is used in a line scanning system in place of a polygon mirror, the HDTV system and a high-definition image system can be used in the line scanning system.
However, when a very small optical mirror is used in a scanning system in place of a polygon mirror, a high-density power light beam which is radiated from a very bright light source for a large screen projection display is reflected from a scanning reflecting mirror surface having a very small area. Therefore, a portion of the high-density power light beam is absorbed by a reflecting mirror medium and is converted into heat. As a result, the temperature of the very small optical mirror system, having a small heat capacity, is increased.
In this way, when the temperature of the reflecting mirror system is increased excessively, component parts of the very small optical mirror are deformed, thereby resulting in the problem that the light-beam scanning system can no longer function as intended.
In addition, when the reflecting mirror is used for a long period of time, its performance is reduced.
Accordingly, in view of such a situation, it is an object of the present invention to make it possible to realize a large display which is low in cost, provides high precision, and achieves high color reproducibility, while restricting deformation and deterioration of a very small optical mirror caused by an increase in temperature thereof.
According to a first aspect of the present invention, there is provided a light scanner including a first scanning unit operable to perform a scanning operation in a first scanning direction as a result of reflecting light beams modulated in accordance with an image signal, the first scanning unit being driven so as to be in synchronization with a high-speed synchronization signal of the image signal; a plurality of light amplifiers operable to amplify the modulated light beams after exiting from the first scanning unit; a light synthesizer operable to synthesize the modulated and amplified light beams into one light beam; and a second scanning unit operable to perform a scanning operation in a second scanning direction as a result of reflecting the one light beam, the second scanning unit being driven so as to be in synchronization with a low-speed synchronization signal of the image signal.
In one form of the first aspect of the present invention, the first scanning unit is a very small optical mirror, and the second scanning unit is a galvanometer mirror.
In another form of the first aspect of the present invention, the first scanning unit performs the scanning operation in a horizontal direction of an image corresponding to the image signal using the modulated light beams.
In still another form of the first aspect of the present invention, an amplifying medium of each light amplifier has the form of a thin plate.
When the amplifying medium of each light amplifier has the form of a thin plate, each amplifying medium may include a rectangular light-incident end upon which the modulated light beams impinge and a rectangular light-exiting end from which the modulated light beams exit.
When the amplifying medium of each light amplifier has the form of a thin plate, each amplifying medium may include first and second areas, the first and second areas being formed of materials having different refractive indices.
When each amplifying medium includes first and second areas, and the first and second areas are formed of materials having different refractive indices, the refractive index of each second area may be smaller than the refractive index of its corresponding first area so as to confine the modulated light beams in the corresponding first area.
When each amplifying medium includes first and second areas, and the first and second areas are formed of materials having different refractive indices, each first area may include a waveguide area and a separation area, each waveguide area including a plurality of channels used to guide and amplify the modulated light beams while maintaining a modulated-light-incident-point mutual relationship, and each separation area preventing coupling between the modulated light beams guided and amplified by adjacent ones of the channels.
When each first area includes a waveguide area and a separation area, each waveguide area includes a plurality of channels used to guide and amplify the modulated light beams while maintaining a modulated-light-incident-point mutual relationship, and each separation area prevents coupling between the modulated light beams guided and amplified by adjacent ones of the channels, each waveguide area may have a greater refractive index than the refractive index of its corresponding separation area; or each separation area may have high absorptivity with respect to at least a corresponding modulated light wavelength.
In still another form of the first aspect of the present invention, the second scanning unit performs the scanning operation in a vertical direction of an image corresponding to the image signal using the one light beam.
In the light scanner of the present invention, after the modulated light is used for the scanning operation in the first direction, the light is amplified. Then, the amplified modulated light is synthesized into one light beam in order for the synthesized light beam to be used for the vertical scanning operation in the second direction.
According to a second aspect of the present invention, there is provided a projection display device including light exiting means for causing light modulated in accordance with an image signal to exit therefrom; first scanning means for performing a first scanning operation in accordance with a high-speed synchronization signal of the image signal using the modulated light that has exited from the light-exiting means; light amplifying means for amplifying the modulated light used for the first scanning operation; light synthesizing means for synthesizing the modulated light amplified by the light amplifying means; second scanning means for performing a second scanning operation in accordance with a low-speed synchronization signal of the image signal using the light synthesized by the light synthesizing means; and display control means for controlling the display of an image that corresponds to the light used for the second scanning operation.
In the projection display device of the present invention, after the modulated light has been used for the first scanning operation at a high speed by the first scanning means, the light is amplified. Then, the synthesized light beam is used for the second scanning operation at a low speed by the second scanning means.
According to a third aspect of the present invention, there is provided a method for scanning light using light beams modulated in accordance with an image signal. According to the method, a scanning operation is performed in a first scanning direction as a result of reflecting the modulated light beams using a first scanning unit, the first scanning unit being driven so as to be in synchronization with a high-speed synchronization signal of the image signal; the modulated light beams are amplified after the first scanning operation; the modulated and amplified light beams are synthesized into one light beam; and a scanning operation is performed in a second scanning direction as a result of reflecting the one light beam using a second scanning unit, the second scanning unit being driven so as to be in synchronization with a low-speed synchronization signal of the image signal.
According to a fourth aspect of the present invention, there is provided a projection display method. The projection display method includes providing light modulated in accordance with an image signal; performing a first scanning operation on the modulated light in accordance with a high-speed synchronization signal of the image signal; amplifying the modulated light after the first scanning operation; operation; synthesizing the modulated and amplified light into one light beam; performing a second scanning operation on the one light beam in accordance with a low-speed synchronization signal of the image signal; and controlling the display of an image that corresponds to the one light beam used for the second scanning operation.